1. Field of the Invention
The present invention relates to subsea system in which grease is delivered to various subsea components of offshore oil and gas production and drilling systems. More particularly, the present invention the relates to grease accumulators having an indicator showing when the accumulator bottle is near empty. Additionally, the present invention relates to automatic accumulator switching systems in which a bottle of grease is automatically actuated when another bottle becomes empty or near-empty.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
As well drilling operations progress into deeper waters in the search for new oil and gas reserves, new subsea equipment must be developed. Valves are the main flow control devices for this equipment. Since handwheel-operated valves cannot easily be used below the surface of bodies of water, hydraulically-actuated valves (and other pressure and flow control devices) are typically used to control the flow of oil and gas from underground reserves.
It is important to be able to provide grease into wireline tooling. The grease provide a seal for such wireline tooling. Ultimately, the subsea tree requires a substantial amount of grease so as to effectively operate.
In the past, it has been necessary to supply grease to such subsea operations by pumping grease through an extremely long umbilical. Typically, the grease will be pumped from the rig to its desired location in the subsea equipment. Unfortunately, it is often difficult to pump the grease through such long umbilicals since the pressure and temperature in deep subsea operations will cause the grease to become too viscous to be effectively pumped. To avoid this problem, it is desirable to pump grease to the equipment from a location as close as possible to the equipment.
In the past, “accumulators” have been used so as to supply fluids to subsea equipment. Pressurized hydraulic fluid is typically generated by high-pressure, low volume, positive displacement pumps. Since a large volume of hydraulic fluid is required to activate most subsea valves, and other pressure control devices, pressurized hydraulic power fluid reservoirs, or “accumulators”, are used in conjunction with the low volume positive-displacement pumps. These accumulators usually takes the form of a hollow metal spherical or cylindrical canister partially-filled with a pressurized inert gas, such as nitrogen, and partially-filled with a pressurized hydraulic fluid. In operation, these accumulators are initially precharged with pressurized nitrogen prior to being submerged. The precharged pressure usually is equal to the anticipated pressure of the water that will be encountered at the depth of submersion of the accumulator. This precharging is necessary to provide a compressible medium that will accept a quantity of power fluid upon charging, and then expel it upon demand.
Grease accumulators have been utilized in the past to supply a grease to the subsea equipment. However, in the past, there has been no way for an operator of such grease accumulators to have any positive knowledge of when the accumulator is near empty. Typically, such grease accumulators are replaced at periodic intervals so as to assure that the grease is continually applied to the subsea equipment. In many circumstances, the accumulators are replaced either too early or too late. If they are replaced too early, then unnecessary operations are required. If the grease accumulators are replaced after they are entirely empty, then there would be an absence of grease flow to the important subsea equipment. If there is an absence of grease supplied to the subsea equipment, the pressure in the well could potentially blow out the equipment. As such, it is very important to continuously supply grease to the subsea components.
Another problem with existing grease accumulators is the fact that the flow of grease must be shut down as the accumulator bottle is replaced. Once again, during the shutdown of the grease accumulator or, during the period of replacement, there is the possibility that the well could blow out by virtue of the pressures applied to the components during the absence of grease flow. As such, it is very important to continuously have a supply of grease flowing to the subsea equipment, even during the replacement of the canisters.
In the past, various patents have issued relating to fluid accumulators for use in subsea applications. For example, U.S. Pat. No. 4,649,704, issued on Mar. 17, 1987 to G. L. Marsh, teaches a pressurized fluid accumulator adapted to be connected to a subsea valve actuator on a drilling wellhead assembly. There is a pressure-compensated piston located in a first hydraulic cylinder. The movement of this piston causes pressurized hydraulic fluid to be delivered in sufficient volume to activate a subsea hydraulically-activated valve. The first piston is connected to and driven by a second piston contained in a second hydraulic cylinder. The charging and accumulation of pressurized hydraulic fluid in the first cylinder causes a nearly absolute vacuum to be developed under the second piston. The pressure differential between this vacuum and the prevailing sea pressure is used to move the first piston during delivery of the hydraulic fluid to the actuator of the hydraulically-activated valve.
U.S. Pat. No. 6,202,753, issued on Mar. 20, 2001 to B. F. Baugh, describes a subsea accumulator and method of operation. This accumulator uses a differential between a high pressure ambient pressure source, such as sea water pressure, and a low pressure source, such as a chamber holding vacuum or atmospheric pressure, to provide storage and delivery of hydraulic power for operation of equipment.
U.S. Patent Publication No. 2007/0240882, published on Oct. 18, 2007 to Leonardi et al., provides an accumulator for subsea equipment. This accumulator apparatus comprises a housing and an accumulator within the housing at the first end of the housing. The accumulator has first and second chambers that are hermetically-sealed from one another. A pressurized gas in the first chamber and a pressurized fluid in the second chamber are arranged within the accumulator. A third chamber in the housing abuts the accumulator and contains silicon oil fluid. A movable piston is located within the housing proximate the second end of the housing. Ambient pressure is communicated to one end of the piston. Ambient pressure plus the pressure in the second chamber is communicated to the second end of the piston. The cross-sectional areas of the two ends of the piston are selected to optimize the pressure at which the piston begins to expel fluid from the second chamber.
U.S. Pat. No. 3,640,299, issued on Feb. 8, 1972 to N. A. Nelson, describes a subsea wellhead control system. This system has a single protective conduit connected at one end thereof to a control facility while its other end terminates in a connection structure located adjacent or attached to a remotely located wellhead. Suitable actuator control conduits extend from a plurality of fluid-controlled wellhead valve actuators and are connected in fluid communication to the connection structure. The valve accumulators are energized by the actuating fluid responsive to actuation of the pilot valves. An accumulator and pressure-balancing circuit are communicated to the fluid circuitry of each of the valve actuators in order to allow quick energized and deenergized actuation of the valve actuators. Fluid pressure is transferred from the accumulator and pressure-balancing circuitry to the actuator fluid supply of the fluid system upon reduction of pressure in the actuator fluid supply and such transfer may be aided by the hydrostatic head of the sea water in which the system is submerged.
U.S. Patent Publication No. 2008/0104951, published on May 8, 2008 to F. B. Springett, shows a subsea pressure accumulator system which has a body with three or more interior chambers. The body has a first body end with a first opening, and a second body end with a second opening. An amount of operational power fluid in the first chamber and an amount of pressurized gas in the second chamber move a piston assembly for moving power fluid from the body to operate an apparatus. The piston assembly has a cavity within a piston end for containing additional pressurized gas for moving the piston assembly.
U.S. Pat. No. 4,036,247, issued on Jul. 19, 1977 to B. F. Baugh, discloses a multi-pressure, single line supply system for purpose of conveying fluid from a single subsea supply conduit in order provide a fluid supply for each of a plurality of subsea well control apparatus that require fluid supplies at different pressure levels. A fluid receiver receives fluid under pressure from the single subsea supply conduit. A regulator regulates fluid flow from the receiver to charge one or more accumulators with fluid at desired pressure levels and to control injection of the fluid through an injection line into a subsea well flowline.
It is an object of the present invention to a grease accumulator apparatus that provides a positive visual indication of when the accumulator is empty or near-empty of grease.
It is another object of the present invention to a grease accumulator apparatus which continuously supplies grease to subsea equipment, even during periods of replacement.
It is another object of the present invention to a grease accumulator apparatus that automatically switches the flow of grease from one accumulator bottle to another accumulator bottle when the first accumulator bottle is near empty.
It is still another object of the present invention to a grease accumulator system which allows for the quick and easy replacement of the accumulator bottle in a safe and efficient manner.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.